Dose proportionality of three different doses of tibolone

Levels of Tibolone and Estradiol and their Nonsulfated and Sulfated Metabolites in Serum, Myometrium, and Vagina of Postmenopausal Women Following Treatment for 21 Days With Tibolone, Estradiol, or Estradiol Plus Medroxyprogestrone Acetate

Tibolone has estrogenic effects on the vagina but not on the uterus. To explain this, levels of tibolone and estradiol and their metabolites were determined in serum, myometrium, and vagina. Thirty-four postmenopausal women with uterine prolapse received either no treatment, tibolone, E(2) or E(2) + medroxyprogesterone acetate (MPA) for 21 days, or a single dose of tibolone. Twenty +/- 6 hours after administration, >98% of the 3-hydroxytibolone metabolites in serum and tissues were disulfated. Of the unconjugated metabolites, the estrogenic 3alpha-hydroxytibolone predominated in serum, whereas the progestagenic/ androgenic Delta(4)-tibolone predominated in myometrium and vagina. Levels of disulfated metabolites in serum and tissues were higher (3- to 5-fold) after multiple dosing than after a single dose. Tissue:serum ratios were <1, except for Delta(4)-tibolone. In all groups, E(2) tissue levels were higher than serum levels; the percentage of serum E(1)S was >90%. Tibolone did not affect endogenous E(1), E(2), or E(1)S levels in serum, but in myometrium and vagina, E(1) levels were significantly higher and E(1)S levels tended to be lower than in controls. Serum and tissue levels of endogenous and exogenous E(1), E(2), and E(1)S were markedly increased 20 hours after E(2) or E(2) + MPA; the percentage of E(1)S and tissue:serum ratios were not affected. MPA had no effect on the degree of sulfation of E(1). Compared with serum, tissue levels of E(2) were high in all groups; absolute E(2) levels in control and tibolone groups were much lower than in the E(2) groups. Tibolone metabolite patterns are different in serum, myometrium, and vagina.

Regulation of activities of steroid hormone receptors by tibolone and its primary metabolites

This work was undertaken (i) to study deeply the estrogen, androgen and progestative activities of tibolone and its metabolites (ii) to determine whether tibolone and its metabolites present glucocorticoid or mineralocorticoid activity. For this purpose, we used human cell lines bearing a luciferase gene with a responsive element under the control of human estrogen receptor alpha (ERalpha) or estrogen receptor beta (ERbeta) or androgen receptor (AR) or chimeric Gal4 fusion with progesterone receptor (PR), glucocorticoid receptor (GR) or mineralocorticoid receptor (MR). The major tibolone metabolites, the two hydroxymetabolites, bind and activate ER with a preference for ERalpha. Tibolone and the Delta(4)-tibolone are agonists for AR and PR and surprisingly 3alpha- and 3beta-OH-tibolone are antagonists for them. Moreover we showed for the first time that tibolone and its primary metabolites are GR and MR antagonists with a stronger affinity for MR than for GR. In conclusion, tibolone by these actions on different receptors and by this capacity to transform in different metabolites, has more complex effects than initially supposed.

Exploratory assessment of dose proportionality: review of current approaches and proposal for a practical criterion

This article reviews currently used approaches for establishing dose proportionality in Phase I dose escalation studies. A review of relevant literature between 2002 and 2006 found that the power model was the preferred choice for assessing dose proportionality in about one-third of the articles. This article promotes the use of the power model and a conceptually appealing extension, i.e. a criterion based on comparing the 90% confidence interval for the ratio of predicted mean values from the extremes of the dose range (R(dnm)) to pre-defined equivalence criterion (theta(L),theta(U)). The choice of bioequivalence default values of theta(L)=0.8 and theta(U)=1.25 seems reasonable for dose levels only a doubling apart but are impractically strict when applied over the complete dose range. Power calculations are used to show that this prescribed criterion lacks power to conclude dose proportionality in typical Phase I dose-escalation studies. A more lenient criterion with values theta(L)=0.5 and theta(U)=2 is proposed for exploratory dose proportionality assessments across the complete dose range.

Sexuality and the menopause

Sexuality is innate within all women to a greater or lesser extent, and is affected by a number of extrinsic factors that occur in the menopausal transition. Assessing hormone status is difficult as evidence exists that sex hormones may differ between ethnic groups, and that bio-assays may be insensitive at lower testosterone levels. Data are available on the prevalence of female sexual dysfunction, but results from cross-sectional studies differ from those of longitudinal studies. The original traditional models of human sexual response have been challenged, and new models have been defined which show more complex interaction between intrinsic and extrinsic factors. Definitions of sexual dysfunction have been redefined. There are a limited number of randomized, placebo-controlled trials of drugs to improve sexual function. These include sildenafil citrate, tibolone and hormone replacement therapy. Randomized controlled trials on testosterone replacement in naturally and/or surgically menopausal patients with female sexual dysfunction have been criticized for a high placebo response rate and short duration. This chapter seeks to put sexuality into perspective and to define both function and dysfunction.

Tibolone rapidly attenuates the GABAB response in hypothalamic neurones

Tibolone is primarily used for the treatment of climacteric symptoms. Tibolone is rapidly converted into three major metabolites: 3 alpha- and 3beta-hydroxy (OH)-tibolone, which have oestrogenic effects, and the Delta 4-isomer (Delta 4-tibolone), which has progestogenic and androgenic effects. Because tibolone is effective in treating climacteric symptoms, the effects on the brain may be explained by the oestrogenic activity of tibolone. Using whole-cell patch clamp recording, we found previously that 17beta-oestradiol (E(2)) rapidly altered gamma-aminobutyric acid (GABA) neurotransmission in hypothalamic neurones through a membrane oestrogen receptor (mER). E(2) reduced the potency of the GABA(B) receptor agonist baclofen to activate G-protein-coupled, inwardly rectifying K(+) (GIRK) channels in hypothalamic neurones. Therefore, we hypothesised that tibolone may have some rapid effects through the mER and sought to elucidate the signalling pathway of tibolone's action using selective inhibitors and whole cell recording in ovariectomised female guinea pigs and mice. A sub-population of neurones was identified post hoc as pro-opiomelanocortin (POMC) neurones by immunocytochemical staining. Similar to E(2), we have found that tibolone and its active metabolite 3 beta OH-tibolone rapidly reduced the potency of the GABA(B) receptor agonist baclofen to activate GIRK channels in POMC neurones. The effects were blocked by the ER antagonist ICI 182 780. Other metabolites of tibolone (3 alpha OH-tibolone and Delta 4-tibolone) had no effect. Furthermore, tibolone (and 3 beta OH-tibolone) was fully efficacious in ER alpha knockout (KO) and ER beta KO mice to attenuate GABA(B) responses. The effects of tibolone were blocked by phospholipase C inhibitor U73122. However, in contrast to E(2), the effects of tibolone were not blocked by protein kinase C inhibitors or protein kinase A inhibitors. It appears that tibolone (and 3 beta OH-tibolone) activates phospholipase C leading to phosphatidylinositol bisphosphate metabolism and direct alteration of GIRK channel function. Therefore, tibolone may enhance synaptic efficacy through the G(q) signalling pathways of mER in brain circuits that are critical for maintaining homeostatic functions.

Bioequivalence studies of tibolone in premenopausal women and effects on expression of the tibolone-metabolizing enzyme AKR1C (aldo-keto reductase) family caused by estradiol

This study aimed to investigate the bioequivalence of a test formulation of tibolone with the marketed reference formulation in 24 young healthy female volunteers. Tibolone is a synthetic steroid hormone for menopausal women. Volunteers were treated with the 2 formulations of tibolone (total dose of active ingredient 2.5 mg) according to a 2 x 2 crossover design with a 1-week washout period. Plasma concentrations of 3alpha- and 3beta-hydroxytibolone, which are major metabolites of tibolone, were assayed in timed samples over a 24-hour period with a validated gas chromatography/mass spectrometry (GC/MS) method that had a lower limit of quantification of 0.5 ng/mL. The reference and test formulations gave a mean 3alpha-hydroxytibolone C(max) of 5.0 and 5.2 ng/mL, respectively, and a mean 3beta-hydroxytibolone C(max) of 16.4 and 16.5 ng/mL, respectively. The mean AUC(t) of 3alpha-hydroxytibolone was 24.7 and 24.3 ng h/mL, whereas the mean AUC(t) of 3beta-hydroxytibolone was 57.6 and 54.8 ng h/mL for the test and reference formulations, respectively. The authors did not find significant differences in pharmacokinetic parameters between the 2 formulations, but metabolite formation was different from reports in postmenopausal women. The authors therefore measured the effects of estradiol on the expression of the tibolone-metabolizing enzymes, from the aldo-keto reductase (AKR1C) family, using HepG2 cell (human hepatoma cells) and MCF-7 cell (human breast cancer cells). Estradiol increased mRNA levels of AKR1C1, AKR1C2, and AKR1C3 and protein levels of total AKR1C in HepG2 cells. Estradiol selectively enhanced levels of AKR1C2 mRNA in MCF-7 cells. Thus, changes in the major metabolites of tibolone might result from changes in AKR1C family expression by patient estrogen status.

Effects of tibolone metabolites on human endometrial cell lines in co-culture

In human endometrium, cell proliferation is regulated by ovarian steroids through heterotypic interactions between stromal and epithelial cells populating this tissue. The authors test the proliferative effects of tibolone and its metabolites using endometrial co-cultures that mimic the normal proliferative response to hormones. They found that both the Delta(4)-tibolone metabolite and the pure progestin ORG2058 counteract estradiol-driven epithelial cell proliferation. Surprisingly, the estrogen receptor binding 3-hydroxyl-metabolites of tibolone also counteracted estradiol-driven proliferation. Inhibition of proliferation by 3beta-OH-tibolone was abrogated by low doses of the progesterone receptor antagonist mifepristone. This suggests that 3beta-OH-tibolone is converted to a progestagenic metabolite. The authors found that the stromal cells used in the co-cultures express high levels of the ketosteroid dehydrogenase AKR1C2, which is able to oxidize 3beta-OH-tibolone back to tibolone. Thus, the unexpected progestagenic effect of 3beta-OH-tibolone in these co-cultures may be due to metabolic activity present in the stromal cells of the co-cultures.

Estrogen and tibolone metabolite levels in blood and breast tissue of postmenopausal women recently diagnosed with early-stage breast cancer and treated with tibolone or placebo for 14 days

Unlike estrogens plus progestagens, tibolone, a selective tissue estrogenic activity regulator, does not increase breast tenderness and mammographic density. To elucidate this, serum and breast levels of tibolone and estrogenic metabolites are measured. Postmenopausal women (n = 102) with early-stage, ER(+ve), primary breast cancer received tibolone or placebo for 14 days in an exploratory, double-blind, randomized trial (STEM carcinoma tissue). Baseline and presurgery sera were collected; tumor tissues were obtained at surgery. E(1) (estrone), E(2) (estradiol), E(1)S (estrone-sulfate), tibolone-its nonsulfated, monosulfated, and disulfated 3-hydroxymetabolites-and Delta(4)-tibolone were measured by validated gas chromatography and mass spectrometry and liquid chromatography with tandem mass spectrometry assays. More than 12 hours after the final dose, serum E(1), E(2), and E(1)S levels were unchanged with placebo, whereas tibolone significantly increased E(1)S and the E(1)S/(E(1) + E(2)) ratio. In tumors, E(1) and E(2) levels were higher than in serum, and E(1)S levels were lower, with placebo and tibolone administration. The percentage of E(1)S was about 90% in serum and 16% in tissue. Tibolone did not affect tissue levels of endogenous estrogens. Serum levels of estrogenic 3alpha- and 3beta-hydroxytibolone, progestagenic/androgenic Delta(4)-tibolone, and monosulfate metabolites were low. Serum 3alphaS,17betaS-tibolone and 3 betaS,17betaS-tibolone levels were 250 and 52 ng/mL, respectively. Tumor levels of 3alpha- and 3beta-hydroxytibolone and Delta(4)-tibolone were higher than in serum, but disulfate levels were lower. The percentage of sulfated tibolone metabolites was 99% in serum and 96% in tumor. Serum metabolite patterns of estradiol and tibolone are different from those in tissues and are compatible with neutral effects of tibolone on breast Ki67 expression.

Cardiovascular Effects of Tibolone: A Selective Tissue Estrogenic Activity Regulator

Traditionally, it was accepted that long-term hormone replacement therapy (HRT) has a cardiovascular beneficial effect in postmenopausal women with and without coronary artery disease (CAD). However, randomized trials in postmenopausal women have not shown any benefit in either primary or secondary prevention of cardiovascular events. Therefore, these findings have raised the question of whether traditional HRT (i.e., estrogen and progesterone) has a cardioprotective effect in women at risk for or with established CAD. Concerns about the use of conventional HRT have led to a search for alternatives. Tibolone is a synthetic compound with estrogenic, androgenic, and progestogenic properties that relieves climacteric symptoms and prevents postmenopausal bone loss. Tibolone possesses a tissue-selective mechanism of action that differs from that of estrogen and/or progestogen. Unlike these compounds, tibolone's metabolites play a central role in its mode of action. Tibolone is widely used for HRT. However, its clinical impact on cardiovascular disease is still under study. The current review focuses on the effects of tibolone on the cardiovascular system and discusses clinical investigations with this compound in postmenopausal women.

7α-Methyl-ethinyl estradiol is not a metabolite of tibolone but a chemical stress artifact

OBJECTIVE

This study was conducted to establish whether 7alpha-methyl-ethinyl estradiol (7alpha-MEE) in plasma from postmenopausal women treated with tibolone is a metabolite or an artifact.

DESIGN

Clinical samples with known levels of tibolone metabolites, plus plasma samples spiked with tibolone and metabolites, were analyzed for levels of 7alpha-MEE using liquid chromatography-mass spectometry (LC-MS/MS) with and without derivatization.

RESULTS

Approximately 20 to 40 pg/mL 7alpha-MEE was detected using LC-MS/MS with derivatization in plasma samples from postmenopausal women treated with tibolone. In plasma samples spiked with 200 ng/mL tibolone or Delta-tibolone, LC-MS/MS with derivatization revealed the generation of around 200 and 36 pg/mL 7alpha-MEE, respectively, whereas LC-MS/MS without derivatization showed no detectable chemical conversion of tibolone to 7alpha-MEE. Generation of 7alpha-MEE is increased by the "stress conditions" used in the derivatization procedure; simply drying the sample also shows this artifactual conversion. The major active and sulfated 3-hydroxy metabolites of tibolone are not converted to 7alpha-MEE. Without derivatization, and avoiding stress conditions, no detectable levels (<20 pg/mL) of 7alpha-MEE were found in plasma samples from postmenopausal women treated with single (eight participants at 13 time points) or multiple (seven participants at 18 time points) doses of tibolone.

CONCLUSIONS

7alpha-MEE is not a metabolite of tibolone but is a chemical artifact generated during analytical procedures with derivatization. Using LC-MS/MS without derivatization, 7alpha-MEE cannot be demonstrated in plasma from postmenopausal women after single or multiple doses of tibolone.

Selective tissue distribution of tibolone metabolites in mature ovariectomized female cynomolgus monkeys after multiple doses of tibolone

Tibolone is a selective tissue estrogenic activity regulator (STEAR). In postmenopausal women, it acts as an estrogen on brain, vagina, and bone, but not on endometrium and breast. Despite ample supporting in vitro data for tissue-selective actions, confirmative tissue levels of tibolone metabolites are not available. Therefore, we analyzed tibolone and metabolites in plasma and tissues from six ovariectomized cynomolgus monkeys that received tibolone (0.5 mg/kg/day by gavage) for 36 days and were necropsied at 1, 1.25, 2.25, 4, 6, and 24 h after the final dose. The plasma and tissue levels of active, nonsulfated (tibolone, 3alpha-hydroxytibolone, 3beta-hydroxytibolone, and Delta(4)-tibolone), monosulfated (3alpha-sulfate,17beta-hydroxytibolone and 3beta-sulfate,17beta-hydroxytibolone), and disulfated (3alpha,17beta-disulfated-tibolone and 3beta,17betaS-disulfated-tibolone) metabolites were measured by validated gas chromatography with mass spectrometry and liquid chromatography with tandem mass spectrometry. Detection limits were 0.1 to 0.5 ng/ml (plasma) and 0.5 to 2 ng/g (tissues). In brain tissues, estrogenic 3alpha-hydroxytibolone was predominant with 3 to 8 times higher levels than in plasma; levels of sulfated metabolites were low. In vaginal tissues, major nonsulfated metabolites were 3alpha-hydroxytibolone and the androgenic/progestagenic Delta(4)-tibolone; disulfated metabolites were predominant. Remarkably high levels of monosulfated metabolites were found in the proximal vagina. In endometrium, myometrium, and mammary glands, levels of 3-hydroxymetabolites were low and those of sulfated metabolites were high (about 98% disulfated). Delta(4)-Tibolone/3-hydroxytibolone ratios were 2 to 3 in endometrium, about equal in breast and proximal vagina, and 0.1 in plasma and brain. It is concluded that tibolone metabolites show a unique tissue-specific distribution pattern explaining the tissue effects in monkeys and the clinical effects in postmenopausal women.

Pharmacokinetic Parameters of Tibolone and Metabolites in Plasma, Urine, Feces, and Bile from Ovariectomized Cynomolgus Monkeys after a Single Dose or Multiple Doses of Tibolone

Levels of nonsulfated and sulfated tibolone metabolites were determined in plasma, urine, and feces from six ovariectomized, mature female cynomolgus monkeys after a single dose and multiple p.o. doses (including bile) of tibolone using validated gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry assays. In plasma, the predominant nonsulfated metabolite after single and multiple dosing was the estrogenic 3alpha-hydroxytibolone; levels of the estrogenic 3beta-hydroxytibolone were 10-fold lower and of progestagenic/androgenic Delta(4)-tibolone, 5-fold lower. Tibolone was undetectable. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone; levels of 3betaS,17betaS-tibolone were about 2-fold lower, and monosulfated 3-hydroxymetabolites were about 10-fold lower. After multiple doses, areas under the curve of nonsulfated metabolites were lower (2-fold), and those of sulfated metabolites were 25% higher. In plasma, >95% metabolites were disulfated. In urine, levels of all the metabolites after single and multiple doses were low. After a single dose, high levels of 3beta-hydroxytibolone and the 3-monosulfated metabolites (3betaS,17betaOH-tibolone and 3alphaS,17betaOH-tibolone) were found in feces. After multiple dosing, 3alpha-hydroxytibolone increased, and the ratio of 3alpha/3beta-hydroxytibolone became about 1. The predominant sulfated metabolite was 3alphaS,17betaS-tibolone. Levels of all the metabolites in feces were higher after multiple doses than after a single dose. Levels of nonsulfated and 3-monosulfated metabolites were higher in feces than in plasma. Bile contained very high metabolite levels, except monosulfates. This may contribute to the metabolite content of the feces after multiple doses. 3beta-Hydroxytibolone and 3alphaS,17betaS-tibolone predominated. In conclusion, tibolone had different metabolite patterns in plasma, urine, feces, and bile in monkeys. The bile contributed to the metabolite pattern in feces after multiple doses. The major excretion route was in feces.

Pharmacokinetic Parameters of Sulfated Tibolone Metabolites in Postmenopausal Women after Single and Multiple Doses of Tibolone

The objective of this study was to determine pharmacokinetic parameters of sulfated tibolone metabolites after single dose and their accumulation after multiple doses of tibolone. Blood samples from postmenopausal women in a single-dose (2.5 mg tibolone), open-label study (n=8) and multiple-dose (placebo, 0.3, 0.625, 1.25, or 2.5 mg/day tibolone for twenty-six cycles of 28 days), randomized, double-blind study (n=15) were analyzed for non-sulfated and sulfated tibolone metabolites by validated gas chromatography-mass spectrometry (GC-MS) and liquid chromatography with tanolam mass spectrometry (LC-MS/MS), respectively. The predominant non-sulfated and sulfated metabolites after a single dose were 3alpha-hydroxy-tibolone and 3alpha,17beta-di-sulfated (di-S)-tibolone. At 3 h, >90% of metabolites were sulfated. Tibolone and Delta(4)-tibolone were detectable for about 6 h. After multiple treatment cycles with different doses, metabolite levels at 10 h were dose-related and levels of di-S metabolites were three- to fivefold higher than after a single dose. Tibolone metabolite levels did not differ between cycles. Inactive di-S tibolone metabolites predominated in blood. No accumulation occurred between cycles 7 and 26.

Estradiol valerate and tibolone: effects on memory

This study investigated the effects of estradiol valerate (EV) and tibolone (TB) treatments on some memory parameters of ovariectomized young (2 months), adult (8 months) and old (20 months) female rats. A Sham-operated group was used as control and the animals were treated daily, by oral gavage, with saline (Sham and placebo NR group), EV (0.3 mg/kg) or TB (0.5 or 1 mg/kg, TB1 and TB2, respectively). In step-down inhibitory avoidance task, the latency of old TB2-treated females in the short-term test was significantly inferior (p<0.05), compared to TB2 adults. In the elevated plus maze, adult NR females spent significantly less time (p<0.05) in the open arms as compared with EV and TB2-treated animals. Additionally, adult TB2-treated females spent significantly less time in the closed arms compared to Sham, NR and TB1 groups. Finally, in the water maze retention test, young TB1-treated animals performed worse when compared to Sham, EV and TB2 females. In the old animals, EV treatment hampered subject performance as compared to all other treatments. Taken together, these results indicate that ovarian hormones differently affect female memory in an age-dependent manner.

Metabolism of exogenous sex steroids and effect on brain functions with a focus on tibolone

Around the menopause, changes in ovarian secretion of steroids result in changes in brain function: hot flushes and sweating later followed by changes in mood, libido and cognition. The relationship between sex steroids and brain functions are reviewed, with focus on hormonal treatments, in particular tibolone, on the postmenopausal brain and on associations between tissue levels and brain functions. Data on steroid levels in human brain are limited. Exogenous oestrogens alone or combined with progestagens reduce hot flushes and sweating, and may favourably affect anxiety, depression and mood. Testosterone alone or combined with E(2) improves libido and mood. Tibolone reduces hot flushes and sweating, and improves mood and libido, but does not stimulate endometrium or breast, like oestrogens. Tibolone is an ideal compound for studying steroid levels and metabolism in brain in view of its structural differences from endogenous steroids and its extensive metabolism required to express its endocrine effects. Brain levels of tibolone metabolites were measured in ovariectomized cynomolgus monkeys receiving tibolone for 36 days. Compared to serum, higher levels of the oestrogenic 3alpha/beta-hydroxytibolone and the androgenic/progestagenic Delta(4)-tibolone, and lower levels of sulphated metabolites are found in various brain regions. The high levels of oestrogenic metabolites in the hypothalamus explain hot flush reduction. Combined with the presence of Delta(4)-tibolone, the tibolone-induced increase in free testosterone through SHBG reduction explains androgenic effects of tibolone on mood and libido. The levels of tibolone metabolites in the monkey brain support tibolone's effects on brain functions.

Beneficial effect of tibolone on mood, cognition, well-being, and sexuality in menopausal women

Tibolone is a synthetic molecule used extensively for the management of menopausal symptoms, with the proposed additional advantage of enhanced mood and libido. Tibolone, after oral administration, is rapidly converted into 3 major metabolites: 3alpha-hydroxytibolone and 3beta-hydroxytibolone, which have estrogenic effects, and the Delta(4)-isomer, which has progestogenic and androgenic effects. The tissue-selective effects of tibolone are the result of metabolism, of enzyme regulation, and of receptor activation which vary in different tissues. Tibolone seems to be effective on estrogen-withdrawal symptoms such as hot flushes, sweating, insomnia, headache, and vaginal dryness, with results generally comparable to the effects exerted by estrogen-based treatments, and the additional property of a progestogenic activity on the endometrium. As well as relieving vasomotor symptoms, tibolone has positive effects on sexual well-being and mood, and improves dyspareunia and libido. These effects may depend on both estrogenic and androgenic actions exerted at the genital level and in the central nervous system, and on a reduction of sex-hormone-binding globulin and an increase of free testosterone, without affecting Delta-5 androgens levels. Based on the evidence available, tibolone is a valuable treatment option to relieve menopausal complaints, especially in women suffering persistent fatigue, blunted motivation, and loss of sexual desire despite an adequate estrogen replacement.

Assessment of DNA damage in postmenopausal women under osteoporosis therapy

OBJECTIVE

The following study was designed to examine possible DNA damage levels in peripheral blood leukocytes, using the alkaline Comet assay, isolated from postmenopausal women undergoing osteoporosis treatment.

STUDY DESIGN

Thirty-two postmenopausal women were randomized into two groups of 16. A dosage of 2.5 mg/day of tibolone (Livial) and 10mg/day of alendronate sodium (Fosamax) were administered to Group 1 over a 12-month period while Group 2 took 10 mg/day of alendronate alone over the same period. The control group consisted of 16 postmenopausal women who did not receive any treatment. Genotoxicity was assessed by the standard method of alkaline Comet assay.

RESULTS

When the results of the study groups were compared with those of the control group, significant differences in terms of DNA damage levels were found (p<0.05). However, no difference was detected between Groups 1 and 2 (p>0.05).

CONCLUSION

Although, no statistical difference in terms of DNA damage levels between tibolone plus alendronate as opposed to alendronate alone was found, an increase in DNA damage levels was observed in Groups 1 and 2 compared with the control group. Consequently, it can be asserted that the frequency of DNA damage in postmenopausal women with osteoporosis increases under alendronate treatment with or without tibolone.

Tibolone and metabolites induce prolactin production in human endometrial stromal cells in vitro: evidence for cell-specific metabolism

In this study, we assessed the effects of tibolone and its metabolites on the production of a progesterone sensitive parameter, prolactin, in human endometrium stroma cells in vitro. In addition, the metabolism of the compounds by isolated stromal and epithelial cells was evaluated. The reference compounds, progesterone, Org 2058, and DHT all induced prolactin production. Oestradiol also slightly induced prolactin production and enhanced the response to Org 2058. Tibolone and Delta4-tibolone were similar with regard to potency to induce prolactin levels in the culture supernatant. Their potency was lower than that of Org 2058, similar to that of progesterone and higher than that of DHT. The efficacies of tibolone, Delta4-tibolone and Org 2058 were similar (approximately 200-fold induction). The estrogenic tibolone metabolites 3alpha- and 3beta-OH tibolone also significantly stimulated prolactin production. Their potency, however, was low since significance was reached only at the highest concentrations tested. The PR antagonist Org 31710 inhibited both tibolone- and Delta4-tibolone-induced prolactin production. The responses of tibolone and Delta4-tibolone were not affected by co-incubation with the androgen receptor antagonist OH-flutamide. The effect of tibolone, but not Delta4-tibolone, was antagonized approximately 50% in combination with the highest dose (1 microM) estrogen receptor antagonist, ICI 164384. The induction of prolactin by 3alpha- and 3beta-OH tibolone was antagonized most potently by Org 31710, but also by ICI 164384 and OH-flutamide. Tibolone is metabolized differently in epithelial and stromal cells of the human endometrium. The epithelial cells mostly produce the progestagenic/androgenic Delta4-tibolone. The stromal cells produce predominantly the 3beta-OH tibolone, and some Delta4-tibolone, but the net effect observed with regard to prolactin production is progestagenic. When the metabolites 3alpha-OH, 3beta-OH, and Delta4-tibolone were added to the cultures no conversions were observed. The HPLC analyses showed no evidence for the production of sulfated metabolites. In conclusion, the net effects on endometrial stromal cells are predominantly progestagenic. Tibolone is converted by epithelial cells into Delta4-tibolone which displays progestagenic and androgenic activities, whereas in stromal cells also the estrogenic metabolites 3alpha- and 3beta-OH tibolone are formed.

Histological and immunohistochemical evaluation of postmenopausal endometrium after 3 weeks of treatment with tibolone, estrogen only, or estrogen plus progestagen

OBJECTIVE

To evaluate histological and immunohistochemical parameters of short-term (21 days) tibolone, estrogen-only, and estrogen+progestagen treatment in the human postmenopausal endometrium.

DESIGN

An observational, open, nonrandomized, controlled study.

SETTING

Three collaborating centers: Amphia Hospital in Breda, Albert Schweitzer Hospital in Dordrecht, Erasmus Medical Center in Rotterdam, the Netherlands.

PATIENT(S)

Thirty healthy, postmenopausal women.

INTERVENTION(S)

Control group (n = 9), no hormonal treatment; tibolone group (n = 8), patients were treated with 2.5 mg of tibolone (administered orally) every day, starting 21 days before surgery; estrogen group (n = 7), patients were treated with 2 mg of E(2) (Zumenon, administered orally; Zambon, Amerfoort; The Netherlands) every day, starting 21 days before surgery; estrogen+progestagen group (n = 6), patients were treated with 2 mg of E(2) (Zumenon, administered orally) and 5 mg of medroxyprogesterone acetate (administered orally) every day, starting 21 days before surgery.

MAIN OUTCOME MEASURE(S)

Uterine tissues were collected, and two pathologists independently assessed histology. Immunohistochemical parameters measured were estrogen receptor alpha, progesterone receptor A/B, Hoxa10, Ki67, and Bcl-2.

RESULT(S)

On the basis of a number of histological and immunohistochemical parameters measured after 21 days of treatment, it was observed that tibolone displays clearly less stimulation (proliferation) of the human postmenopausal endometrium than estrogen at the beginning of a treatment, but the stimulation is higher than with estrogen+progestagen.

CONCLUSION(S)

Short-term (21 days) tibolone treatment results in a small stimulation of proliferation of the endometrium, and because long-term treatment with tibolone has been demonstrated to lead to an atrophic endometrium, it may be concluded that the stimulatory effect, as observed in this study, is transient in nature. It is hypothesized that tibolone first displays a more estrogenic mode of action, which over time, is counterbalanced by the induction of its progestagenic properties.

Effect of tibolone administration on central and peripheral levels of allopregnanolone and beta-endorphin in female rats

OBJECTIVE

We evaluated the effects of tibolone oral administration on neuroendocrine function by investigating the modulation exerted by tibolone administration on allopregnanolone and central and peripheral beta-endorphin (beta-EP) levels in ovariectomized rats.

DESIGN

Female Wistar rats (N = 64) were included: 48 rats were ovariectomized, 8 cycling rats were included as controls, and 8 cycling rats were treated with placebo. The ovariectomized animals were divided into six groups: untreated rats and those that received 14-day oral treatment with either placebo, estradiol valerate (E2V) 0.05 mg/kg/d, or tibolone (0.1, 0.5, or 2 mg/kg/d. beta-EP levels were assessed in the frontal lobe, parietal lobe, hippocampus, hypothalamus, anterior pituitary, neurointermediate pituitary, and plasma, whereas allopregnanolone levels were measured in the frontal lobe, parietal lobe, hippocampus, hypothalamus, anterior pituitary, adrenal glands, and serum.

RESULTS

The administration of tibolone (0.5 and 2 mg/kg/d) in ovariectomized rats induces a significant increase of allopregnanolone in the frontal lobe, parietal lobe, hippocampus, hypothalamus, whereas in serum a significant increase of allopregnanolone occurs only with the dose of 2 mg/kg/d, a significant decrease in allopregnanolone levels occurs in the adrenal glands. No changes occurred in the anterior pituitary. Tibolone doses of 0.5 and 2 mg/kg/d induced a significant increase in beta-EP content in the frontal lobe, hypothalamus, and neurointermediate lobe; and, at doses of 2 mg/kg/d, in the parietal lobe, anterior pituitary, and plasma, without changes in the hippocampus. Compared with E2V, 0.5 mg/kg/d tibolone showed a similar effect on allopregnanolone and beta-EP in most brain regions.

CONCLUSIONS

Tibolone administration affects beta-EP and allopregnanolone levels, playing a role as a neuroendocrine modulator.

Endothelium-dependent dilatory effects of 3α-OH-tibolone in gracilis muscle arterioles of the female Wistar rat

OBJECTIVE

Tibolone is a synthetic steroid used for the treatment of the symptoms of menopause that, once metabolized, has estrogenic, progestogenic, and androgenic properties. We investigated the direct vasodilatory effects of the major active tibolone metabolite 3alpha-OH-tibolone and its sulfated form on female rat skeletal muscle arterioles, which play an important role in the control of blood pressure.

DESIGN

In isolated, pressurized spontaneously constricted arterioles (mean passive diameter 83 +/- 3 microm), we investigated the vasodilatory effect of 3alpha-OH-tibolone and its sulfated form. To study the role of the endothelium and in particular that of nitric oxide, we repeated the experiments with 3alpha-OH-tibolone after removal of the endothelium and on vessels pretreated with the nitric oxide synthesis inhibitor, Nomega-nitro-L-arginine (L-Na). Finally we compared the vasodilatory effect of 3alpha-OH-tibolone with 17beta-estradiol.

RESULTS

A dose-dependent dilatation to 3alpha-OH-tibolone was observed starting at a concentration of 10 M. With the sulfated form of 3alpha-OH-tibolone, dilatation was only present at the highest concentration (10 M). In the denuded vessels, the vasodilatory effect was absent at concentrations from 10 to 10 M. The dilatation induced by 3alpha-OH-tibolone was not significantly reduced by L-Na. The vasodilatory effect of 3alpha-OH-tibolone did not differ from that of 17beta-estradiol.

CONCLUSIONS

3alpha-OH-tibolone has a dose-dependent vasodilatory effect on isolated skeletal muscle arterioles from the rat. The sulfated form has no vasodilatory effect in this setup. This finding suggests that during this short incubation time there was no conversion of the sulfated metabolite into its active form by the vascular endothelium. The vasodilatory effect of 3alpha-OH-tibolone is endothelium dependent at physiologic concentrations and comparable to that of 17beta-estradiol.

Tissue-selective effects of tibolone on the breast

Hormone treatment with an estrogen plus a progestagen (EPT) increases the risk of breast cancer. Both hormone activities are also induced by tibolone. In order to assess the breast safety of tibolone, it was evaluated in several pre-clinical models. The effects were inconclusive in breast cancer cell lines but, in various in vivo models, it did not stimulate the breast. In the 17,12-dimethylbenz(a)anthracene (DMBA) model, tibolone clearly inhibited the growth of breast tumors and, when given prophylactally, far less tumors developed. Ovariectomized monkeys showed no increase in the expression of the proliferation marker Ki67. The effects of tibolone and its metabolites on the steroid metabolizing enzymes in breast tissues were investigated in order to unravel its mode of action in the breast. Tibolone and its metabolites did not inhibit aromatase, but sulfatase was profoundly inhibited. The sulfated 3alpha-OH tibolone metabolite even showed irreversible inhibition of sulfatase. In addition, 17ss-hydroxysteroid dehydrogenase activities were slightly inhibited and sulfotransferase activity was stimulated at low concentrations. The consequence of these effects is that, for both endogenous estrogens and estrogenic-metabolites of tibolone, the equilibrium is preferential for the sulfated forms. The intracellular hormonal milieu tibolone and its metabolites also influence cellular homeostasis. It inhibits cell proliferation of normal breast epithelial cells and stimulates apoptosis. In this respect, tibolone behaves differently from estrogens. Clinical studies have shown that tibolone users experience less breast tenderness and do not show an increase in mammographic density as found with continuous combined EPT. The data concerning tibolone and breast cancer risk are inconclusive and require further investigation.

Tissue-selectivity: the mechanism of action of tibolone

Tibolone is effective in preventing bone loss and treating climacteric symptoms, without stimulating the endometrium. The effects on bone, brain and vagina can be accurately explained by the oestrogenic activity of tibolone, but oestrogenic activity is not expressed in the endometrium. Tibolone behaves differently from oestrogen plus progestogen combinations on the breast. Therefore, tibolone can be characterised as a selective oestrogen activity regulator. The objective of this review is to characterise the typical properties of tibolone in order to explain its tissue-selective action. Tibolone is rapidly converted into three major metabolites: 3 alpha- and 3 beta-hydroxy-tibolone, which have oestrogenic effects, and the Delta(4)-isomer, which has progestogenic and androgenic effects. The 3-hydroxy metabolites are present in the circulation, predominantly in their inactive sulphated form. The tissue-selective effects of tibolone are the result of metabolism, enzyme regulation and receptor activation that vary in different tissues. The bone preserving effects are the result of oestradiol receptor activation, whilst other steroid receptors, notably the progesterone and androgen receptor, are not involved. Breast tissue of monkeys is not stimulated, as occurs with oestrogen plus progestogen, because tibolone and its metabolites inhibit sulphatase and 17 beta-hydroxysteroid dehydrogenase (HSD) type I and stimulate sulphotransferase and 17 beta-HSD type II, the combined effects of which prevent conversion to active oestrogens. In addition, tibolone affects cellular homeostasis in the breast by inhibiting proliferation and stimulating apoptosis. Tibolone does not stimulate the endometrium because of the action of the highly stable progestogenic metabolite (Delta(4)-isomer) in combination with an effect on the sulphatase (inhibition)-sulphotransferase (stimulation) system. The oestrogenic metabolites of tibolone have direct favourable effects on the cardiovascular system and, in in vivo models, tibolone has shown no adverse consequences. In conclusion, tibolone shows oestrogenic effects in brain, vagina and bone and has direct oestrogenic effects on the cardiovascular system. In the endometrium, the progestogenic activity of the Delta(4)-metabolite and the effect on oestrogen-inactivating enzymes prevent oestrogenic stimulation. The mammary gland is not stimulated in currently used animal models. Tibolone appears to regulate estrogenic activity in the various tissues by influencing the availability of estrogenic compounds for the estradiol receptor in a tissue-selective manner.

Effect of renal impairment on the pharmacokinetics of a single oral dose of tibolone 2.5 mg in early postmenopausal women

STUDY OBJECTIVE

To determine the influence of renal function on the pharmacokinetics of tibolone and its primary metabolites, delta4-tibolone, 3alpha-hydroxytibolone, and 3beta-hydroxytibolone.

DESIGN

Open-label, single-center, single-dose study

SETTING

Drug research center, Balatonfüred, Hungary.

SUBJECTS

Twenty-four postmenopausal women aged 45-65 years.

INTERVENTION

Subjects were assigned to one of four groups based on their renal function, as assessed by glomerular filtration rate (normal to severely impaired), and received a single dose of tibolone 2.5 mg. Pharmacokinetic parameters of tibolone and its primary metabolites were derived from blood samples taken at predefined intervals for up to 48 hours after tibolone administration. Pharmacokinetic parameters were calculated using standard noncompartmental methods and compared by analysis of covariance.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic parameters of tibolone and its primary metabolites were similar in subjects with normal to severely impaired renal function. Pharmacokinetic profiles of tibolone and its metabolites were independent of the degree of renal impairment.

CONCLUSION

Pharmacokinetic parameters of tibolone were not affected by varying degrees of renal function.